Zephyr RTOS
An open-source real-time operating system with native BLE stack, used by Nordic's nRF Connect SDK and many BLE SoC vendors.
Zephyr RTOS
Zephyr is an open-source, vendor-neutral real-time operating system (RTOS) with a native, fully integrated BLE protocol stack. Maintained by the Linux Foundation, Zephyr has become the de facto standard RTOS for BLE product development, adopted by Nordic Semiconductor's nRF Connect SDK, Intel, and dozens of other silicon vendors.
BLE Stack Architecture
Zephyr's BLE implementation includes both host and controller components:
- Controller: Link Layer, PHY management, advertising engine, connection state machine. Runs as a high-priority thread with deterministic timing
- Host: L2CAP, ATT, GATT, SMP, GAP. Runs as application-context threads with callback-based APIs
- HCI driver: Connects host and controller via in-process function calls (single-chip) or UART/SPI transport (dual-chip like nRF5340)
The stack supports BLE 5.4 features including Extended Advertising, Periodic Advertising, Direction Finding, LE Audio (CIS/BIS), and Connection Subrating.
Key Features for BLE Development
Zephyr provides several capabilities critical for BLE firmware:
- Kconfig: Fine-grained compile-time configuration of the BLE stack (disable unused features to save flash/RAM)
- Devicetree: Hardware description for multi-board portability
- Bluetooth Shell: Interactive command-line interface for testing BLE operations without custom firmware
- Logging subsystem: Structured logging with SoC with antenna on a PCB." data-category="Hardware & Implementation">module-level filtering
- MCUboot integration: Secure bootloader for OTA firmware updates
- Bluetooth Mesh: Full Bluetooth Mesh 1.1 support including Directed Forwarding
Supported Hardware
Zephyr supports over 600 boards, including all major BLE SoC families:
- Nordic: nRF52832, nRF52840, nRF5340, nRF54L15, nRF54H20
- Espressif: ESP32-C3, ESP32-C6 (experimental)
- STMicro: STM32WB series
- Silicon Labs: EFR32 (via HAL)
Getting Started
The typical Zephyr BLE development workflow involves:
- Install the Zephyr SDK and
westmeta-tool - Select a sample application (e.g.,
samples/bluetooth/peripheral_hr) - Configure via
prj.conf(Kconfig) and board-specific overlay - Build:
west build -b nrf52840dk/nrf52840 - Flash:
west flash - Debug:
west debugor RTT console
For teams already using Nordic chips, the nRF Connect SDK (which is built on Zephyr) provides Nordic-specific additions including Bluetooth qualification listings, power optimization libraries, and production-quality LE Audio support.
Related Terms
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